1. Field of the Invention
The present invention relates to paving blocks and, in particular to a paving block formed in part from rubber crumb and a method of manufacturing the same.
2. Description of the Related Art
Millions of tires are discarded every year in the United States. The United States Environmental Protection Agency estimated that in 2003 alone approximately 290 million tires were discarded in the United States. It is not desirable to send the discarded tires to landfills because large volumes of tires can rapidly fill the limited space available at the landfills. There is accordingly an ongoing need reduce the number of used tires sent to landfills. One solution is to process the discarded tires to produce crumb rubber which are granules of vulcanized tire rubber with the steel and fibre removed.
It is known to produce crumb rubber through mechanical stepwise grinding or a cryogenic freezing process. In the mechanical process, tires are shredded or cut into smaller pieces which are put through granulators to separate and remove loose steel and fibre. The remaining vulcanized rubber granules are ground in a cracker mill to produce crumb rubber of a desired mesh size. In the cryogenic process, tires are shredded or cut into smaller pieces which are frozen in liquid nitrogen as they pass through a cryogenic tunnel. The frozen tire pieces then pass through a series of cracker mills where they are shattered into their three component parts, namely, rubber, steel and fabric. The cryogenic process is generally more expensive but produces smoother and smaller granules of crumb rubber.
The primary use of crumb rubber is in rubberized asphalt which is a paving material comprised of asphalt concrete mixed with rubber crumb. However, crumb rubber may be used in other applications including pathways, ground cover under playground equipment, resilient flooring in recreational facilities, running tracks, and synthetic turf fields. Crumb rubber has also been used in modular paving blocks.
U.S. Pat. No. 6,602,586 issued on Aug. 5, 2003 to Kakimoto et al. discloses a paving block designed to be paved on an underlying base to absorb impacts. The block includes rubber chips mixed with a resin binder to form a powdery rubber-containing layer which integrally overlays a vulcanized rubber base. The powdery rubber-containing layer functions to absorb impacts and the rubber chips preferably include crumb rubber.
U.S. Pat. No. 7,344,334 issued on Mar. 15, 2008 to Thorkelson discloses a paver system including at least one substrate and a plurality of paving blocks. Each of the paving blocks has a bottom surface configured to engage a top surface of the substrate, thereby preventing lateral movement of the paving blocks. The paving blocks and substrate may be formed from 20 to 80 mesh rubber crumb and a plastic which acts as a binder and forms a matrix for the crumb rubber.
United States Patent Application Publication Number 2009/0297267 published on Dec. 3, 2009 to Glynn discloses a paving block formed of at least crumb rubber and binder. The paving block is a cast block which is preferably formed by hot melt molding or hot pressure molding. Each block has at least one protruding male connector and one recessed female connector. The female connector is configured to receive a male connector of a similar block, thereby allowing adjacent paving blocks to be connected.